This invention relates to circuit breakers in which overload sensing is accomplished electromagnetically by a sensing device which permits the circuit breaker to actuate after a time delay period at certain overloads and with substantially no time delay at other overloads. Such circuit breakers are illustrated, for example, in U.S. Pat. No. 2,360,922, issued to Kurt W. Wilckens, and U.S. Pat. No. 3,329,913, issued to William W. Camp.
These prior patents disclose an electromagnetic sensing device including a solenoid coil, a time delay tube housing a movable core of magnetizable material movable against the retarding action of a liquid to provide a time delay upon the occurrence of an overload and a pivotal, spring biased, armature. If the overload current is below a certain value and if it does not persist for a predetermined time, it will not cause tripping by the armature of the circuit breaker's operating mechanism and will not open the circuit breaker contacts, thereby avoiding nuisance tripping. However, if the overload current is sufficiently high, the resulting magnetic flux will substantially instantaneously cause the armature to pivot and trip the circuit breaker operating linkage mechanism, opening the circuit breaker contacts substantially instantaneously, i.e., with no intentional time delay.
It is the usual practice to construct and adjust such a circuit breaker so that it will carry the rated current without tripping. The circuit breaker may trip when the current is above 100% of rated current and below 125% of rated current after a time delay period. The circuit breaker must trip when the current is 125% of rated current or above (after a time delay period below very high overloads). The circuit breaker will trip substantially instantaneously (with no intentional delay) at substantially higher overloads, for example, 800% of rated current.
The trip point adjustment has heretofore been made by adjusting the spring tension biasing the armature attracted arm away from the pole piece of the solenoid coil and by adjusting the air gap between the attracted arm and the pole piece.
It is an object of this invention to provide a means to variably adjust the trip point of the circuit breaker without varying the spring tension on the armature.
It is another object of this invention to provide a means for adjusting the trip point of the circuit breaker from outside the circuit breaker so that the trip point may be adjusted after the circuit breaker has been fully assembled.
It is a further object of this invention to provide a one piece device of simple and economical construction for externally adjusting the trip point of the circuit breaker.